As a conventional valve timing varying device, there is known a valve timing varying device including a housing rotor (a driving-side rotor) rotated in synchronism with a crankshaft, a vane rotor (a driven-side rotor) rotated in synchronism with a camshaft and accommodated in the housing rotor to divide an accommodating chamber thereof into a retarded angle chamber and an advanced angle chamber and relatively rotatable relative to the housing rotor within a predetermined operating angle (an angle range between a most advanced angle position and a most retarded angle position), a coiled torsion spring installed between the housing rotor and the vane rotor in order to rotation-urge the vane rotor toward an advanced side, a lock mechanism (a lock piece and a spring) for locking the vane rotor in a predetermined position relative to the housing rotor when stopping and starting the engine and for releasing the lock by an oil pressure, and the like (see Patent document 1).
In the device, the housing rotor has a three-divided structure which consists of a cylindrical member covering an outer peripheral area of the vane rotor, a rear side cover member joined with a rear side of the cylindrical member, and a front side cover member joined with a front side of the cylindrical member. Therefore, the number of parts is increased, the man-hour for assembling is increased, and it causes an increase in cost.
Further, the torsion spring is disposed in an accommodating space formed between the vane rotor and the housing rotor in an interior of the device, one end of the torsion spring is latched (or hooked) on the vane rotor and another end of the torsion spring is latched (or hooked) on the housing rotor. Therefore, upon assembling of the device, in case that the front side member is fastened to the cylindrical member while sandwiching the torsion spring between the vane rotor and the front side cover member, (the one end and the another end of) the torsion spring is not visible. Therefore, it is not easy to assemble the front side cover member to the cylindrical member while latching the one end of the torsion spring on the vane rotor and latching the another end of the torsion spring on the housing rotor (the front side cover member). Furthermore, in case that a two-divided structure that the cylindrical member and the front side cover member are integrally formed is adopted for simplification of the structure, it is more difficult to assemble the torsion spring.
And, as another conventional variable valve timing device, there is known a variable valve timing device including a housing rotor (a housing) rotated in synchronism with a crankshaft, a vane rotor rotated in synchronism with a camshaft and accommodated in the housing rotor to divide an accommodating chamber thereof into a retarded angle chamber and an advanced angle chamber and relatively rotatable relative to the housing rotor within a predetermined operating angle (an angle range between a most advanced angle position and a most retarded angle position), a torsional coiled assist spring for rotation-urging the vane rotor toward an advanced side, a cylindrical bushing for holding the assist spring, a lock mechanism (a lock pin and a spring) for locking the vane rotor in the most advanced angle position relative to the housing rotor when stopping and starting the engine and for releasing the lock by an oil pressure, and the like (see Patent documents 2 and 3).
In the device, the housing rotor has a two-divided structure consisting of a bottomed cylindrical front housing member that accommodates the vane rotor, and a plat-like rear side housing member that is joined with the front side housing member so as to cover a rear side opening of the front side housing member. Therefore, simplification of the structure in the housing rotor can be accomplished. On the other hand, the assist spring is assembled in a manner that the coil part (winding portion) is accommodated in the interior of the bushing fitted in the vane rotor thorough the opening of the front housing member, the one end is fitted in a fitting hole of the bushing and a fitting hole of the vane rotor, and the another end is latched on a fixed pin protruding from an outer front face of the housing rotor.
Therefore, even though the assist spring can be assembled while viewing the one end and the another end, a distance from a center of the vane rotor to the another end in a direction of the rotation axis of the camshaft becomes longer since the another end of the assist spring is located in a position where protrudes forwardly from the housing rotor and therefore, an inclination (a deviation) (relative to the rotation axis) of the vane rotor is promoted, the inclination (the deviation) of the vane rotor causes wear of the bearing portion and an increase of a friction force and therefore, a performance deterioration might be caused.
Further, since the fixed pin for latching (or hooking) on the another end of the assist spring is provided on the front face of the outer side of the housing rotor, a size of the device as a whole in the direction of the rotation axis becomes larger, a requirement of downsizing is not met.
Furthermore, since the cylindrical bushing for accommodating the coil part of the assist spring and the fixed pin provided on the housing rotor and the like are required, there arise problems such that components accompanying the assist spring increase, the structure becomes more complex, and the cost becomes higher.